The accurate separation of tumor tissue from non-tumor tissue is a prerequisite for laboratory molecular analysis of many types of tumor tissues.
In standard laboratory practice, tumor tissue for analysis is obtained by cutting a thin tissue section from a formalin fixed, paraffin embedded (FFPE) tissue block known to contain tumor and non-tumor tissue, and preparing the tissue section on a glass histology slide. The tissue section will usually be cut with a thickness of 10-40 μm to allow the outline of tissue structures to be made out by viewing the slide under a standard laboratory microscope.
In order to determine a boundary of a tumor region of a tissue section, it has been proposed to prepare a histology slide with the tissue section, comprising staining the tissue section with a laboratory dye and covering with a glass cover slip according to standard laboratory practice, for viewing and analysis by a trained pathologist.
A method of marking tumor regions of the tissue section comprises the pathologist viewing the slide using a standard laboratory microscope and, based on subjective assessment, for example based on memory or on visual comparison with a look-up chart, identifying regions of the tissue section appearing to correspond to model tumor structures, and indicating boundaries of the regions via a manual annotation with a marker pen on the glass coverslip. Following annotation, a sequential tissue section, preferably having a thickness in the range indicated above, can be cut from the tissue block for further testing.
It is often desirable to test tissue samples to identify the type of a cancerous or other pathological tissue that may be present. The sensitivity of these tests may depend upon the relative and absolute quantity of cancerous or pathological tissue in the sample, for example the number and percentage of tumor cells in the tissue. This is a complex evaluation, as there are many cell types within a given tissue sample and even in regions of the sample which are predominantly tumor, a mixture of non-tumor and normal cells can be found.
Such is the complexity of the pathology image, this task is normally carried out subjectively by an experienced pathologist who visually estimates the % tumor cells within the sample or within a defined region of the sample. This visual estimation can be highly inaccurate